Re: [PATCH 1/2] firmware: cs_dsp: Remove async regmap writes

[Richard Fitzgerald <rf@opensource.cirrus.com>]

On 25/02/2025 3:15 pm, Mark Brown wrote:
> On Tue, Feb 25, 2025 at 01:18:42PM +0000, Richard Fitzgerald wrote:
> 
>> The async writes are a 12-year-old workaround for inefficiency of
>> synchronous writes in the SPI subsystem. The SPI subsystem has since
>> been changed to avoid the overheads, so this workaround should not be
>> necessary.
> 
> That wasn't really the issue, it was that on systems with low numbers of
> slower cores (especially single core but there were some dual core
> systems too) there was a surprisingly low threashold where it was useful
> to overlap the marshalling of data to send to the device with
> transmitting already marshalled data.  SMP adds locking requirements
> which loose a lot of the gains, and it's controller dependent where the
> cuttoff points for interrupts and/or DMA are.

Ok. It was a very long time ago.
Do you want a V2 with a commit message that doesn't libel the SPI
framework?

FWIW switching to sync write reduced the download of small amp firmware
by 200ms on a 1.67MHz SPI bus.